add underscore to postgres fetching

Author: Sergey Kvasha

lib/dialects/postgresql/operators/fetching.js

@@ -1,5 +1,7 @@
 'use strict';
 
+var _ = require('underscore');
+
 module.exports = function(dialect) {
 	dialect.operators.fetching.add('$json', {
 		fn: function(value, end) {